The present disclosure relates to wireless signal processing techniques of generating an in-phase signal and a quadrature signal using a quadrature detector from a signal obtained by mixing a radio frequency signal and a local oscillation signal.
A well-known receiver multiplies a received radio frequency signal by a local oscillation signal, which is a complex signal, using a quadrature detector (i.e., a mixer) to perform quadrature detection, and processes the complex signal obtained after the quadrature detection. Such processing is widely generally known (see D. Weiner et al., The Image Rejection Harmonic Mixer, IEEE MTT-S DIGEST, 1982, pp. 36-38).
An in-phase signal and a quadrature signal, which form the complex signal after the quadrature detection, ideally have the same amplitude and are orthogonal. Actually, however, an error in the orthogonality and the amplitude may exist between the in-phase signal and the quadrature signal, which is also referred to as IQ imbalance. If such an error exists, in the complex signal after the quadrature detection, a desired signal is influenced by an image signal to degrade the quality of the desired signal. In order to address the problem, for example, frequency converters, etc., adjusting the phases and the amplitudes of in-phase signals and quadrature signals output from mixers are suggested (see Japanese Unexamined Patent Publication Nos. 2002-246847, 2003-309612, and 2004-72532).